1. Field of the Invention
The present invention relates to an image processing apparatus, and more particularly to method and apparatus for changing a size of a digital image with a desired magnification.
2. Description of the Prior Art
A facsimile machine having a variable line density function has been known. It has a function which permits it to receive an original document of a size B4 and output it onto a form of a size A4. It, therefore, changes a magnification to produce a size A4 image from a size B4 image.
In the magnification changing method of this machine, a magnification of an optical system for reading density information of an image from an original document is changed in accordance with a size of the original document to be transmitted.
In this machine, the optical system is complex, which prevents cost reduction and compactness of the machine.
A word processor has a character generator pattern stored in a memory and displays or records characters by using a character generator. In an image processing apparatus, the size of the character pattern is usually fixed but there is a demand for various sizes of characters to prepare a document.
It may be attained by storing patterns of various sizes of characters in the memory. However, this requires a large capacity of memory.
In order to resolve the above problem, it has been proposed to store a pattern of one size of characters in the memory and change the size of the pattern by electrical means.
In one of the proposed methods, an image is divided to change a magnification ("Method for Expanding and Reducing a Kanji Pattern" by Inoue et al., Paper of Image Engineering Study Group, Institute of Electronics and Communication of Japan IE79-1, pp. 1-10, 1979).
In this method:
(1) The size of a pattern stored in a memory is 36.times.36 pixels.
(2) For changing a magnification, a 2.times.2 or 3.times.3 pixel matrix is used as a unit to divide the image.
(3) Magnifications are fixed to 3/2 and 4/3.
(4) Patterns of divisional images and patterns of magnified images are paired and stored in a memory. In changing the magnification, the pattern to which the divisional image belongs is determined and is replaced by a paired magnified pattern.
The above method has the following drawbacks.
(1) It cannot be applied to any size of image because the image size is fixed.
(2) It cannot be applied to any magnification of conversion because the magnification is fixed.
(3) It requires dividing the image in a matrix and determining the pattern to which the divisional image belongs. Therefore, processing is complex and high speed processing is not attained.